The present invention relates to a method of producing a profiled product having fins such as an impeller or a runner for use in a centrifugal compressor, a radial turbine and the like.
The impeller of the type described above is in general constituted by a back shroud and a plurality of vanes fixedly secured to or integral with the shroud and extending substantially linearly radially from the rotary axis of the shroud or extending outwardly from the rotary axis in curved form toward the direction of rotation or in the opposite direction. Further, an inducer and an exducer are often provided at the inlet end and the outlet end of each vane, respectively, by appropriately bending the same so as to obtain required inflow and outflow angles at the respective ends.
As a method of producing an impeller as described above, a method by which vanes are formed by machining or cutting a material for forming vanes integral with the shroud, a method by which vanes produced separately from the shroud are fixedly secured thereto, forging method and casting method were known.
Since vanes of an impeller are, however, formed in various configurations as described above, the possibility exists that a die casting method using a split-type mould can not be adopted for producing an impeller when the configuration of vanes constitutes so called undercuts. In such a case, a plaster mould, a sand mould, a lost-wax mould or the like having collapsible cores must be used in general. A casting method using such a mould has disadvantages in that the workability and the productivity are very low in comparison with the die casting method. The cost is high, while the dimensional accuracy and the surface quality of the product are low.